For example, in an inverter that drives a three-phase AC motor, a conventional signal transmission circuit used in a driving circuit device for a power semiconductor switching element in the inverter has the following arrangement.
The conventional signal transmission circuit transmits first and second input signals having different signal velocities while electrically insulating them, and includes a pulse generation unit, first and second transmission units, a latch circuit, and an oscillation determination circuit. The first and second transmission units transmit first and second pulse signals, generated by the pulse generation unit in accordance with the logical states of the first and second input signals, to the latch circuit and the oscillation determination circuit while electrically insulating the signals. The latch circuit obtains a first restoration output signal by restoring the first input signal in accordance with rising edges of the first and second pulse signals. The oscillation determination circuit obtains a second restoration output signal by restoring the second input signal on the basis of the oscillation states of the first and second pulse signals. A signal transmission circuit having such an arrangement is disclosed in, for example, Patent Document 1.